Apache Kudu Security

Kudu includes security features which allow Kudu clusters to be hardened against access from unauthorized users. This guide describes the security features provided by Kudu. Configuring a Secure Kudu Cluster lists essential configuration options when deploying a secure Kudu cluster. Known Limitations contains a list of known deficiencies in Kudu’s security capabilities.

Authentication

Kudu can be configured to enforce secure authentication among servers, and between clients and servers. Authentication prevents untrusted actors from gaining access to Kudu, and securely identifies the connecting user or services for authorization checks. Authentication in Kudu is designed to interoperate with other secure Hadoop components by utilizing Kerberos.

Authentication can be configured on Kudu servers using the --rpc-authentication flag, which can be set to required, optional, or disabled. By default, the flag is set to optional. When required, Kudu will reject connections from clients and servers who lack authentication credentials. When optional, Kudu will attempt to use strong authentication. When disabled or strong authentication fails for 'optional', by default Kudu will only allow unauthenticated connections from trusted subnets, which are private networks (127.0.0.0/8,10.0.0.0/8,172.16.0.0/12,192.168.0.0/16, 169.254.0.0/16) and local subnets of all local network interfaces. Unauthenticated connections from publicly routable IPs will be rejected.

The trusted subnets can be configured using the --trusted_subnets flag, which can be set to IP blocks in CIDR notation separated by comma. Set it to '0.0.0.0/0' to allow unauthenticated connections from all remote IP addresses. However, if network access is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized access. This can be mitigated if authentication is configured to be required.

When the --rpc-authentication flag is set to optional, the cluster does not prevent access from unauthenticated users. To secure a cluster, use --rpc-authentication=required.

Internal PKI

Kudu uses an internal PKI system to issue X.509 certificates to servers in the cluster. Connections between peers who have both obtained certificates will use TLS for authentication, which doesn’t require contacting the Kerberos KDC. These certificates are only used for internal communication among Kudu servers, and between Kudu clients and servers. The certificates are never presented in a public facing protocol.

By using internally-issued certificates, Kudu offers strong authentication which scales to huge clusters, and allows TLS encryption to be used without requiring you to manually deploy certificates on every node.

Authentication Tokens

After authenticating to a secure cluster, the Kudu client will automatically request an authentication token from the Kudu master. An authentication token encapsulates the identity of the authenticated user and carries the master’s RSA signature so that its authenticity can be verified.

This token will be used to authenticate subsequent connections. By default, authentication tokens are only valid for seven days, so that even if a token were compromised, it could not be used indefinitely. For the most part, authentication tokens should be completely transparent to users. By using authentication tokens, Kudu takes advantage of strong authentication without paying the scalability cost of communicating with a central authority for every connection.

When used with distributed compute frameworks such as Spark, authentication tokens can simplify configuration and improve security. For example, the Kudu Spark connector will automatically retrieve an authentication token during the planning stage, and distribute the token to tasks. This allows Spark to work against a secured Kudu cluster where only the planner node has Kerberos credentials.

Scalability

Kudu authentication is designed to scale to thousands of nodes, which requires avoiding unnecessary coordination with a central authentication authority (such as the Kerberos KDC). Instead, Kudu servers and clients will use Kerberos to establish initial trust with the Kudu master, and then use alternate credentials for subsequent connections. In particular, the master will issue internal X.509 certificates to servers, and temporary authentication tokens to clients.

Encryption

Kudu allows all communications among servers and between clients and servers to be encrypted with TLS.

Encryption can be configured on Kudu servers using the --rpc-encryption flag, which can be set to required, optional, or disabled. By default, the flag is set to optional. When required, Kudu will reject unencrypted connections. When optional, Kudu will attempt to use encryption. Same as authentication, when disabled or encryption fails for optional, Kudu will only allow unencrypted connections from trusted subnets and reject any unencrypted connections from publicly routable IPs. To secure a cluster, use --rpc-encryption=required.

Kudu will automatically turn off encryption on local loopback connections, since traffic from these connections is never exposed externally. This allows locality-aware compute frameworks like Spark and Impala to avoid encryption overhead, while still ensuring data confidentiality.

Coarse-Grained Authorization

Kudu supports coarse-grained authorization of client requests based on the authenticated client Kerberos principal (i.e. user or service). The two levels of access which can be configured are:

Superuser - principals authorized as a superuser are able to perform certain administrative functionality such as using the kudu command line tool to diagnose or repair cluster issues.
User - principals authorized as a user are able to access and modify all data in the Kudu cluster. This includes the ability to create, drop, and alter tables as well as read, insert, update, and delete data.

Internally, Kudu has a third access level for the daemons themselves. This ensures that users cannot connect to the cluster and pose as tablet servers.

Access levels are granted using whitelist-style Access Control Lists (ACLs), one for each of the two levels. Each access control list either specifies a comma-separated list of users, or may be set to * to indicate that all authenticated users are able to gain access at the specified level. See Configuring a Secure Kudu Cluster below for examples.

The default value for the User ACL is *, which allows all users access to the cluster. However, if authentication is enabled, this still restricts access to only those users who are able to successfully authenticate via Kerberos. Unauthenticated users on the same network as the Kudu servers will be unable to access the cluster.

Web UI Encryption

The Kudu web UI can be configured to use secure HTTPS encryption by providing each server with TLS certificates. See Configuring a Secure Kudu Cluster for more information on web UI HTTPS configuration.

Web UI Redaction

To prevent sensitive data from being exposed in the web UI, all row data is redacted. Table metadata, such as table names, column names, and partitioning information is not redacted. The web UI can be completely disabled by setting the --webserver-enabled=false flag on Kudu servers.

Disabling the web UI will also disable REST endpoints such as /metrics. Monitoring systems rely on these endpoints to gather metrics data.

Log Security

To prevent sensitive data from being included in Kudu server logs, all row data is redacted by default. By setting the --redact=log flag, redaction will be disabled in the web UI but retained for server logs. Alternatively, --redact=none can be used to disable redaction completely.

Configuring a Secure Kudu Cluster

The following configuration parameters should be set on all servers (master and tablet server) in order to ensure that a Kudu cluster is secure:

# Connection Security
#--------------------
--rpc-authentication=required
--rpc-encryption=required
--keytab-file=<path-to-kerberos-keytab>

# Web UI Security
#--------------------
--webserver-certificate-file=<path-to-cert-pem>
--webserver-private-key-file=<path-to-key-pem>
# optional
--webserver-private-key-password-cmd=<password-cmd>

# If you prefer to disable the web UI entirely:
--webserver-enabled=false

# Coarse-grained authorization
#--------------------------------

# This example ACL setup allows the 'impala' user as well as the
# 'nightly_etl_service_account' principal access to all data in the
# Kudu cluster. The 'hadoopadmin' user is allowed to use administrative
# tooling. Note that, by granting access to 'impala', other users
# may access data in Kudu via the Impala service subject to its own
# authorization rules.
--user-acl=impala,nightly_etl_service_account
--superuser-acl=hadoopadmin

Further information about these flags can be found in the configuration flag reference.

Known Limitations

Kudu has a few known security limitations:

Custom Kerberos Principal: Kudu does not support setting a custom service principal for Kudu processes. The principal must be 'kudu'.
External PKI: Kudu does not support externally-issued certificates for internal wire encryption (server to server and client to server).
Fine-grained Authorization: Kudu does not have the ability to restrict access based on operation type or target (table, column, etc). ACLs currently do not support authorization based on membership in a group.
On-disk Encryption: Kudu does not have built-in on-disk encryption. However, Kudu can be used with whole-disk encryption tools such as dm-crypt.
Web UI Authentication: The Kudu web UI lacks Kerberos-based authentication (SPNEGO), so access cannot be restricted based on Kerberos principals.
Flume Integration: Flume integration is not supported with secure Kudu clusters which require authentication or encryption.